I think you are referring to the Dissenter extension. IIRC it was developed by Gab and it was quickly denigrated by the woke internet. Google and Mozilla blocked it and called it a tool "for right wing extremists to graffiti any web page". I don't know if it is still alive or available, but it relies on a large pool of users to be of any use anyway. There are other such tools for this kind of commenting that are very much alive, but in the wake of the Dissenter smearing, these other "any page" comment tools are probably all moderated and filtered by tyrannical SJW mods.